Motivated by challenges encountered in wireless communication over time-variant channels such as Doppler dispersion or equalization, a new modulation technique termed orthogonal time frequency space (OTFS) was introduced in [1]}. The driving idea behind OTFS is to utilize the delay-Doppler (DD) domain to represent information-carrying symbols. The interaction of the corresponding OTFS waveform with a time-frequency (TF) dispersive channel results in a two-dimensional convolution of the symbols in the DD domain [2]}. OTFS thus turns a time-variant channel into a time-invariant interaction in the DD domain.
The time-invariant waveform-channel interaction is utilized by OTFS and allows to outperform orthogonal frequency division multiplexing (OFDM) in many scenarios, as shown in [1]}, [4]}, [5]}, [2]}, [7]}, [8]}.
